Since print systems have been in existence, printers have sought methods for inhibiting counterfeiting and unauthorized copying of printed documents. Enhanced complexity in an engraved pattern of a press plate is one such method that most people are familiar with as a result of its everyday observation in currency bills. Bank checks, security documents, bonds and other financial documents are other examples of printed documents having complex background patterns to inhibit unauthorized reproduction. Identification documents, e.g. passports, social security cards and the like, are other examples. Credit cards not only have complex background patterns, but now also have embedded holographics to enhance verification and authentication of such a card.
As far as printed documents are concerned, a common complex background pattern is a guilloché line pattern, i.e., an ornamental pattern or border consisting of lines flowing in interlaced curves. FIG. 5 is a check pattern exemplifying a guilloché. The guilloché patterns are designed to be hard to reproduce and thus can serve as a security feature. Information can be embedded in the complexity of the patterns that can be used for many different purposes, which include authentication (e.g. comparing an embedded name information with a name on a check), process control (e.g. routing a check) and banking automation (e.g. recording the dollar amount of a check into a user's account).
There are two main issues in guilloché mark generation. First, a guilloché mark requires creation of a base pattern with two-dimensional (2D) periodicity. This is often difficult with existing graphical tools. Secondly, a pattern modulation to adjust a base pattern and associated replicate patterns is often performed on bitmaps, which sometimes produces visually unpleasing artifacts in the resulting adjusted line patterns, such as uneven curve thickness and abrupt transitions.
The creation of a guilloché mark starts with the 2D periodic pattern. By definition, the mark comprising a plurality of such patterns can be generated by repetition of a rectangular base pattern such as shown in FIG. 5, which is the enlarged base pattern comprising the guilloché mark of FIG. 6. The base pattern has to have a property of repeat symmetry. Specifically, there should be no artificial discontinuity if two base patterns are placed next to each other, whether in a horizontal or vertical direction.
Currently known graphical tools for generating such guilloché marks, and the base patterns thereof, make it difficult to design a pattern such as shown in FIG. 5, which when replicated, produces a pleasing space filling pattern without breaks such as FIG. 6. When drawing any line, the interaction of that line with all its periodic replicates has to be considered in the design. With known standard design tools, this is very difficult, since the periodic nature of the pattern is not explicit in such tools.
Once a base pattern is designed, a set of templates can be created such that each template resembles the base pattern in general, but is different from the base pattern in minute details. Specifically, in such known implementations, a grid is imposed on the bitmap of the base pattern. A template, same size as the basic pattern, is generated by locally shifting the base pattern as follows: (1) if the pixel is on an interior grid point (m, k), the pixel is shifted by two random numbers, [r_x(m,k), r_y(m,k)], in x and y directions, respectively; (2) if the pixel is on a boundary (non-interior) grid point, no shift is performed; (3) if the pixel is not on the grid, its shift is an interpolation of the shifts of its four nearest neighboring grid points. The template generated by the above procedure is a slightly distorted version of the basic pattern. By varying random numbers, N templates can be produced, where N is the number of different symbols to be embedded. The templates produced by such a procedure are generally acceptable in terms of image quality and detection rate. However, a careful examination reveals that visually unpleasant artifacts commonly do exist. Such artifacts can include uneven curve thickness and occasional sharp transitions in originally smooth curves. Applying random numbers with smaller amplitude may reduce the artifacts, but it will also compromise the detection accuracy.
There is a need for a base pattern generation tool that can preserve the desired continuity between adjacent replicate patterns when so shifted for creating such a plurality of N templates.
Another problem with the known systems is that the bitmap adjustment fails to provide a real-time, contemporaneous adjustment of a base pattern for designing a new guilloché mark in a manner that allows the designer to assess the overall mark quality, and to confirm the avoidance of any undesired artifacts. The ability to generate such a mark on-the-fly would avoid delays and inconsistencies resulting from bitmap shifting techniques for adjusting a base pattern.
There is thus a need for a system and method for creating guilloché marks that comprise a tool for generating a base pattern that can be replicated in the mark in a manner that avoids undesired artifacts, maintains line consistency, and which allows a mark designer to assess the results of the creative efforts in real-time.